Magnetic recording media in which a magnetic layer comprising ferromagnetic powder dispersed in binder is provided on nonmagnetic supports are widely employed in computer tapes and disks. In recent years, in the field of magnetic recording, the practice of digital recording, with its low recording deterioration, has developed from conventional analog recording. The recording of a larger volume of signals is generally required in digital recording than in analog recording, moreover, the recording and reproduction devices and the recording media employed are required to provide good picture and sound qualities as well as higher density recording as a result of the demand for smaller size and saving of space.
Recording signal wavelengths are being shortened and recording tracks are being narrowed to achieve high-density recording. Further improvement in electromagnetic characteristics is necessary in recording media. To improve electromagnetic characteristics, various methods such as improving magnetic characteristics of ferromagnetic powders, reducing the particle size, increasing the fill rate, and rendering the medium surface ultrasmooth have been proposed. However, these techniques have not been adequate to achieve the greater densities demanded in recent years.
When the recording wavelength is further shortened and the magnetic layer remains thick, the problems of self-demagnetization loss during recording and thickness loss during reproduction become pronounced. Further, the magnetic layer is being thinned to prevent saturation of the reproduction head. However, when the magnetic layer thickness is reduced to about 0.1 μm or less, the effects of the nonmagnetic support tend to appear on the surface of the magnetic layer, tending to affect electromagnetic characteristics and increase the error rate.
It is important to reduce the size of the magnetic material to reduce noise. Ferromagnetic metal powder with a major axis length equal to or less than 80 μm and ferromagnetic hexagonal ferrite micropowder with a plate diameter equal to or less than 40 nm are employed. However, such microgranular ferromagnetic powder tends to aggregate, and relative to the comparatively large ferromagnetic powder that has been employed thus far, tends to be much more difficult to disperse well.
Accordingly, it is an object of the present invention is to provide a magnetic recording medium having excellent dispersibility, smoothness and electromagnetic characteristics.
The present inventors conducted extensive research for achieving the above-stated object. As a result, they discovered that by employing microgranular magnetic material and a binder of prescribed polar group content in at least one magnetic layer, dispersibility of the microgranular ferromagnetic powder was improved, and moldability in the calendering step conducted to improve smoothness of the magnetic layer was improved; the present invention was devised on this basis.